It's quite difficult to say if a story is well written or not, since in the end the acting might influence in a good or bad way. Sometimes the dialogue is well written, but the acting is terrible and that ends up destroying everything.
But anyway, one drama I thought the storyline was well written was Shiroi Kyotou (white tower). It was such an interesting drama!
As for hana yori dango, I must say I disliked it...

iswak had great direction and a great cast, plus it was smart to work with the original material and not try to change it around(unlike the jdrama version)...plus the extra scenes added more to it that added to the story than take away from it...it could have easily failed but it made someone like me who does not understand any mandarin enjoy it and laugh---if there was bad writing, i would have stopped watching after the second episode or even earlier

In fact, when I first heard the name, i thought it would be some corny love story and thought it would suck, but it was good and the actors acted like real people---I can't stand exaggerated acting---my usual issue with most jdramas

Plus undeniable chemistry b/w Ariel Lin and Joe Cheng...U almost wonder if they're a couple in real life---Even if they are not, they look good together and should do another well-written drama together for my and other fans' amusement--and i'm loving the sequel already

I like dramas that has good story line and good dialogues. It helps catch attention specially in romantic dramas. Most dramas that came from mangas are really great (mostly Jdrama). Its new and fast paced, interesting and unexpected events.

Mars is definitely one of the best scripts. It's a very deep and meaningful drama with a lot of plot to it. Nobuta wo Produce is also one very well written drama. The author had a really strong hold on the meaning of friendship, that really brought you to tears in the end.